Prior art workers have devised numerous methods for making filled articles from curable, moldable material. The filled articles, themselves, range from golf ball centers and tennis balls, on the one hand, to encapsulated medicaments and contraceptive devices on the other.
One approach to the forming of filled articles is exemplified by U.S. Pat. No. 1,146,523 in the name of F. T. Roberts, issued July 13, 1915, and U.S. Pat. No. 2,223,019 in the name of J. R. Gammeter, issued Nov. 26, 1940 and U.S. Pat. No. 2,329,839 in the name of P. Kalowski, issued Sept. 21, 1943. The latter two patents teach the making of golf ball centers. Both patents involve the forming of hollow rubber balls in two halves, and joining the halves together while immersed in a liquid filling material. U.S. Pat. No. 1,146,523 teaches a method for making inflated rubber articles wherein the hollow rubber article is made in two parts which are joined together while located within a chamber filled with compressed air, the balls being thereafter cured and trimmed of flash.
Yet another approach is taught in U.S. Pat. No. 2,249,612 in the name of P. Kalowski, issued July 15, 1941. In accordance with this reference, a golf ball center is manufactured by drawing a raw rubber sheet into a cup-shaped member. The cup-shaped member is filled with a liquid filling material. The filled cup-shaped member is then capped by a further sheet of raw rubber. This structure is thereafter placed in a perfectly spherical mold and is vulcanized and cured to form the golf ball center.
U.S. Pat. No. 1,163,987 in the name of W. J. Eggers, issued Dec. 14, 1915 and U.S. Pat. No. 1,263,141 in the name of H. R. Strauss, issued Apr. 16, 1918 both teach methods wherein spherical rubber balls are made in two halves. The halves are joined together and the resulting balls are filled with fluid by means of a needle or the like, prior to or during a vulcanizing step.
U.S. Pat. No. 3,773,871 in the name of E. W. Merril, issued Nov. 20, 1973, teaches a process for encapsulating drugs and other therapeutic reagents which can be effused through the encapsulating material. According to this reference two blanks of circular disk-like configuration are formed from uniformly thick sheeted silicone gum stock. These disks are each placed in a shaped mold so as to form a depression in its center portion. This center portion is then subjected to direct ionizing radiation to cross link the polymer. The central depressed portion of each blank is thereafter filled with medicament and the blanks are assembled face to face with the medicament encapsulated therebetween. Gentle pressure is applied to the flange portion of the structure to cause coalescence between the silicone in the flanges. Thereafter, the flange portion of the device is subjected to ionizing radiation so that the flange portion becomes uniformly cross linked.
The method of the present invention for making filled articles from curable polymeric material has many and varied applications. For purposes of an exemplary showing, the process will be described in its application to the manufacture of vaginal contraceptives of the general type taught in U.S. Pat. No. 4,198,976 in the names of J. L. Drobish and T. W. Gougeon, issued Apr. 22, 1980 and U.S. Pat. No. 4,200,090 in the name of J. L. Drobish, issued Apr. 29, 1980.
The teachings of the two last mentioned patents are incorporated herein by reference. Briefly, these references teach devices used in the vagina to deliver spermicidal surfactant. The contraceptive of each of these references is foldable for easy insertion and, once in position at the cervical os, it opens to "cap" the os and remain in position, even during intercourse, so that access of the spermicidal surfactant source to the cervical os is not interrupted. The contraceptive is designed to remain comfortably in the vagina during the time between menstrual periods to provide desirable, prolonged release of a spermicidal surfactant.
In general, the contraceptive of each of these references comprises two dome-shaped or dish-shaped disks which are assembled into an externally rimless structure constituting a container for the spermicidal ingredient. The front or inner face of the device (that surface facing the os) constitutes a membrane permeable by surfactant monomers but not permeable to the passage of surfactant micelles. The outer or rearward portion of the device is less permeable (or impermeable) to surfactant monomers by virtue of being made of a different material, or by being made of the same material and of greater thickness than the front or inner face. The two parts of the device are assembled with their edges sealed together in any suitable fashion such as polymer welding, adhesive sealing, or the like. The completed unit is filled through a thick section using a hypodermic syringe. As a part of this step, air trapped in the unit during sealing has to be bled back into the syringe.
An important feature of the contraceptive devices of these references lies in the fact that each provides a reservoir from which spermicide is released in a controlled manner through the semi-permeable membrane which comprises at least a portion of the inner or front face of the device. The material from which the device is made is such that surfactant micelles cannot diffuse through the semi-permeable membrane. Rather, they must first disassociate to form surfactant monomer molecules which then dissolve in the membrane material and diffuse therethrough to its outer surface. Once so diffused, the surfactant monomers are free to dissolve in the surrounding vaginal fluid to provide their contraceptive effect. The predominant driving force for this diffusion is the concentration difference between unassociated (i.e., substantially monomeric) surfactant molecules in the solution inside and outside the contraceptive device. As a result, the rate of transport through the membrane will slow drastically when the exterior surfactant monomer concentration approaches that on the interior of the device, resulting in the desired controlled release of the surfactant through the membrane. The bulk of the surfactant remains in micellar form, where it resides in reserve within the device to provide a source of monomers over a long period of time, thereby delivering continuous contraceptive protection to the user for a time period of from about 20 to about 30 days.
The method of manufacture taught in the above noted references, comprising the steps of molding an inner or front part and an outer or rear part; gluing the parts together with an appropriate adhesive; filling the completed unit with a hypodermic syringe, and bleeding trapped air back into the syringe, was a slow process which did not lend itself well to commercialization. The present invention is based upon the discovery of a form-fill-seal and cure (where thermosetting materials are employed) process which can be performed in one rapid sequence without removing the unit from its original forming molds. This process is very much faster, dramatically reducing processing time. A more consistent and higher quality product is obtained. Typically less scrap is produced and the process enables more design latitude, since the entire process is carried out without removing the unit from its original forming molds prior to completion.
The process of the present invention enables the forming of uncured parts by compression or injection molding and the joining and curing of these parts to form a hollow filled or unfilled article. The joining step incorporates pinch-off of excess material forming a strong, reinforced, leak-free line seal which is smooth and flash-free at the exterior of the product. While it is generally preferred to maintain the seal area free of extraneous materials, this seal can in some instances be accomplished even when surfactant solutions and mold release agents are present in the seal area as the molds are closing. When the device is to be filled with a liquid, or the like, a novel purge and partial vacuum procedure is provided to minimize the volume of gas in the final cavity and the presence of gas bubbles in the walls of the unit, to eliminate frothing of the active filler material, and to provide a proper balance of liquid and gas within the unit to serve as a strong, resilient, compression molding core.